1. Field of the Invention
The present invention relates to an apparatus for electrically controlling the output of an AC generator for use in a vehicle.
2. Description of the Prior Art
FIG. 4 is a circuit diagram of a controller for a car AC generator disclosed by Japanese Laid-open Patent Application No. 7-298515. In FIG. 4, reference numeral 1 denotes an AC generator mounted on a vehicle, which comprises an armature coil 101 for generating an AC output and a field coil 102 driven by an unshown internal combustion engine mounted on the vehicle. Denoted by 2 is a rectifier for rectifying the AC output of the AC generator 1, which comprises an output terminal 201 for the excitation of the field coil 102 and the voltage detection of a voltage regulator 3 and an output terminal 202 for grounding. The voltage regulator 3 is for controlling the output voltage of the AC generator 1 to a predetermined value. Reference numeral 4 represents a battery mounted on the vehicle, 5 a key switch and 6 a charging display lamp.
A description is subsequently given of the operation of the above controller. When the key switch 5 is closed at the start of the internal combustion engine, a base current is supplied from the battery 4 to a transistor 313 through the key switch 5, the charging display lamp 6 and a fixed resistor 301 so that the transistor 313 becomes conductive. Then, the base current is supplied to a transistor 314 through a fixed resistor 302 so that the transistor 314 becomes conductive. Thereby, the base current is supplied to a transistor 321 so that the transistor 321 becomes conductive, whereby a field current runs into the field coil 101 from the battery 4 to enable the AC generator 1 to generate power. When the internal combustion engine starts operation in this state, the field coil 102 turns and the armature coil 101 generates 3-phase AC induced electromotive force.
When the AC generator 1 begins to output a 3-phase AC, the rectifier 2 rectifies the 3-phase AC and converts it into a DC. Then, the voltage regulator 3 receives the output voltage of the output terminal 201 of the rectifier 2. When a potential divided by a fixed resistor 305 and a fixed resistor 306 exceeds a predetermined value, a zener diode 319 and a transistor 320 become conductive and a base current to the transistor 321 is cut off so that the transistor 321 becomes nonconductive, whereby a field current from the battery 4 to the field coil 102 is cutoff and the output voltage of the AC generator 1 drops.
When the output voltage of the AC generator 12 drops and the potential divided by the fixed resistor 305 and the fixed is resistor 306 falls below the predetermined value, the Zener diode 319 and the transistor 320 become nonconductive, the transistor 321 becomes conductive, a field current runs from the battery 4 to the field coil 102, and the output voltage of the AC generator 1 rises. Thus, after the start of the internal combustion engine, the voltage regulator 3 controls the output voltage of the AC generator 1 to a predetermined value by repeating the conductive state and nonconductive state of the transistor 321 alternately.
When the charging display lamp 6 is disconnected or a display lamp drive terminal gets out of place, even if the key switch 5 is closed, the transistors 314 and 314 are both nonconductive before the start of the internal combustion engine. Therefore, the transistor 321 is nonconductive. If some residual magnetic flux is existent in the field coil 102 in this state, the AC generator 1 outputs a slight amount of voltage by the start of the internal combustion engine. When the single-phase voltage of the AC generator 1 is charged into a capacitor 317 through a fixed resistor 304, the transistor 313 becomes conductive through fixed resistors 308 and 301. As a result, the transistor 314 becomes conductive, the AC generator 1 outputs a normal voltage in the same manner as during the normal operation of the charging display lamp 6, and the output voltage of the AC generator 1 is controlled to the predetermined value by the function of the voltage regulator 3.